(i) Field of the Invention
The present invention relates to a method of digitizing a locus data in a profiling method, and apparatus constructed so that so model shape is converted to an NC block data train, which is an approximate locus, by a profiling machine and the data is used to perform NC working by a working machine.
(ii) Prior Art Statement
Generally, the digitizing operation in the above apparatus is linearly approximated with a certain tolerance and when the tolerance is exceeded, the block data is cut out. By repeating this procedure, the block data train approximating surface position of a model has been obtained.
In order to attain profiling working with high accuracy heretofore in the above method, when the tolerance is set to a small value such as 0.01 mm, it is disadvantageous that the block data is numerous. When a shape of a model is complicated or when a surface of a model is rough, the number of the block data is necessarily increased. However, another large cause is overlap of noise-like variation component to dot-train data. This contains fluctuation of about several microns of a position detection system of the profiling machine and a noise component contained in a displacement signal of a tracer head. Adding the fluctuation and the component, they exceed the tolerance in the worst case and the digitizing operation with high accuracy can not be attained. A known low-pass filter is used to remove the fluctuation component and particularly there are many examples in which application is made to the displacement signal of the tracer head. In order to obtain the surface position of the model exactly, it is necessary to sample a machine position signal and the displacement signal of the tracer head at the same time and add them. However, a delay time of the low-pass filter causes an error in a calculation position of the model surface. This becomes a problem particularly upon the high speed profiling operation.
In this manner, the prior art working operation using the digitizing operation is considered that slightly rough tolerance is used or numerous block data is indispensable if tolerance is set strictly. However, requirement of high accuracy in the profiling working is recently enhanced increasingly and the digitizing method with high accuracy is now desired. However, there is no effective method heretofore.